The present invention relates to valves, and more particularly to stop valves for controlling fluid flow through pipelines, such as subterranean or over ground pipes for fluid flow, e.g. water and gas pipes.
There are many miles of water and gas pipelines located underground in the UK, and indeed elsewhere in the world. Valves are located at many points along these pipelines, to enable control of the flow of fluid through sections of the pipelines adjacent the valves. For example, many large diameter pipes are located deep underneath roadways, from which smaller diameter pipes branch off, each leading to separate industrial, commercial or residential properties to supply them with e.g. tap water or other non-treated forms of water. Should there be a water leak at one of these properties, a valve in the branch pipe to that property can be operated to stop the flow of water from the large diameter main pipe to the residence along the branch pipe.
These valves can take one of many forms, but essentially each has some sort of internal barrier member, such as a gate, a ball, a plug, or a disc (in the case of a butterfly valve), which is moveable to allow, to restrain, or to stop the flow of fluid through the valve. Such barrier members are usually moved by rotating a spindle which extends from the barrier member to the exterior of the valve, towards the ground level above the valve.
To operate one of these subterranean valves, an operative feeds a tool, e.g. tee-bar, valve key down an open shaft from ground level, which open shaft extends down to the valve. The operative aims to locate the end of their key on an e.g. tapered or shaped shank on the end of the spindle. Then, by rotating the key, the spindle is turned, thus moving the barrier member of the valve, to block or unblock the channel in the valve through which the fluid flows. Alternatively, the spindle of the valve may extend the majority of the way up the open shaft from the valve to the ground surface, allowing the service engineer to use a short key on the end of the long spindle to operate the valve.
In either case, such an open shaft cannot be left open to the elements since such an opening in a footpath or roadway poses a significant danger to pedestrians and drivers, etc. Thus, a cover plate is located in the roadway or footpath above the valve to cover the open shaft. As these cover plates usually need to withstand the weight of traffic passing over them, including heavy goods vehicles, it is preferred to make the cover plates as small as possible. Small cover plates need not be made as robust as larger ones to withstand the same mass.
Of course, these valves require maintenance, for example to replace a part of the closing mechanism of the valve after it becomes worn or damaged. In known pipelines, once the section of pipeline in which a valve is located is isolated from the rest of the pipeline network (perhaps by closing valves upstream and downstream of the valve in question), or the pipeline is depressurised, the valve can be serviced. Conventional valves have a removable ‘bonnet’ on their upper side (the term ‘upper’ is used here with reference to the relative orientation of the valve to the road surface above) which is held onto the main casing of the valve by a number of bolts to cover an access chamber in the valve. In many valves, once the bonnet has been removed, the closing mechanism of the valve can be accessed and removed for such servicing. In some cases the closing mechanism is of a closed-type, such as a plug valve, but such a valve still requires the removal of the outer bonnet to access the plug.
In order to be able to remove such a bonnet, a service engineer must be able to access the valve itself. Since the valves in question are located deep underground, e.g. 2 to 15 feet (0.6 m to 4.5 m) below ground level, this is not possible from the road surface. Also, the cover plate in the road surface and the underlying open shaft are too narrow to allow a service engineer to climb down. Thus, maintenance on such subterranean valves can only be carried out after excavation of the earth, tarmac, etc. above the valve, which is of course time consuming, expensive and highly inconvenient to pedestrians and motorists who, as a result of such excavation, may find roads closed or partially blocked with temporary traffic control systems in operation.
There are also several types of overland (above ground) valves which require the removal of a bonnet to access an access chamber within the valve for maintenance purposes. Although not requiring excavation, as in the case of subterranean valves, such a removal of a bonnet is time consuming, and thus costly.
Thus, there is a need for a valve that is suitable for subterranean use yet which has a flow control mechanism that can be serviced from ground level without the need to excavate the ground above and around the valve. There is also a need for an overland valve which can be quickly and cheaply serviced.
It is often necessary to carryout monitoring operations in fluid carrying pipelines. Monitoring may only be required from time to time, and hence it would be desirable to provide an apparatus into which a monitoring device may be fitted, yet easily be removed.